Unfortunately some electronic components cannot deal with speed enhancement of a wideband gap semiconductor under present circumstances. One of the electronic components is a Zener diode. The Zener diode starts to pass a current when a predetermined voltage or more is applied in a reverse direction, and a voltage at both ends of the Zener diode is kept constant. Therefore, the Zener diode is used for various purposes such as gate protection of a reference-voltage generating circuit and an FET and removal of a surge mixed from a power supply line.
However, in the Zener diode, a reference voltage changes by a current passed therethrough. This means that, when the Zener diode is connected to a power source containing a ripple, the current passed through the Zener diode changes by a power fluctuation and therefore the reference voltage fluctuates. In the case where an impedance of a load connected to an output of the reference voltage changes by the Zener diode, the output of the reference voltage becomes unstable because the current passed through the Zener diode changes. Because the reference voltage is generated by an avalanche breakdown, sometimes a large noise becomes troublesome. The Zener diode is mainly made of a Si semiconductor, and the high-speed operation of the Zener diode cannot be performed by factors such as a junction capacitance and slow hole mobility generated by a PN junction.